1. Field of the Invention
This invention relates generally to a polarizer/modulator assembly for a laser and, more particularly, to a polarizer/modulator assembly for a solid state diode laser, including an independently removable polarizer unit and modulator unit, where the polarizer unit corrects for beam polarization when the polarizer unit is moved into the beam path and absorbs the light that is reflected from the polarizer and removes the resultant heat.
2. Discussion of the Related Art
High-power, solid state lasers, such as diode pumped slab lasers, that are used for many purposes, such as cutting, drilling and welding of various materials, electronics manufacture, medical treatment, nuclear fusion, laser weapons, etc., are known in the art. A solid state slab laser will include one or more gain modules having a solid state laser gain medium, such as a crystal of neodymium yttrium aluminum garnet (Nd:YAG), Yb:YAG, Ti:Sapphire or neodymium glass (Nd: Glass), and an optical pumping source to produce a population inversion in the gain medium. The gain medium typically has a slab configuration with a rectangular cross-section and optically polished major side and end faces. The optical pumping source generally is an array of diodes positioned adjacent to the side faces of the slab. The laser gain medium absorbs radiation from the diodes to create a population inversion within the medium to produce a laser output. The end faces of the slab are preferably formed at a non-perpendicular angle to the side faces so that light travels longitudinally in a zig-zag pattern through the laser gain medium as it is reflected off of the side faces. The diodes are switched on and off in a controlled manner to generate a square-wave pulsed laser beam emitted from the gain medium. The light output of the diode arrays can be accurately tuned to the absorption line of the active material of the laser gain medium to achieve a high pumping efficiency. A high power solid state slab laser of this type is disclosed in U.S. Pat. No. 5,555,254 issued to Injeyan et al., Sep. 10, 1996 and U.S. patent application Ser. No. 08/683,585, filed Jul. 15, 1996, titled Diode Laser Pumped Solid State Laser Gain Module, and assigned to the assignee of the instant invention.
The laser beam generated by the gain module discussed above typically is elliptically polarized when it is emitted from the gain module because of the configuration of the slab. Because the beam is elliptically polarized, it sometimes needs to be linearly polarized depending on the particular use or application of the beam. For example, if the laser is to be used for a cutting or drilling process, then an elliptically polarized beam is undesirable because the beam will not provide the best available laser/material interaction for these applications. To improve the interaction, the beam is first linearly polarized, and is then optically rotated to provide a circularly polarized beam suitable for these applications. If the laser is being used for a welding process, non-coherent or elliptically polarized light is suitable, and thus the beam is generally not polarized so as to eliminate loss of beam intensity by the polarization process. Different laser designs and different applications have different polarization requirements.
Additionally, it is sometimes desirable to modulate the beam to provide high peak power for cutting and drilling applications. It is necessary that the laser beam be polarized before it is modulated. The modulator modulates the relatively long, square-wave beam pulses to provide short duration beam pulses (such as on the order of 100 nanoseconds) having a relatively high peak power, for example on the order of 500 kilowatts, that provides greater precision and control for certain applications. In one example, the laser beam pulses generated by the high power solid state laser gain module are modulated by an acousto-optical modulator that provides the modulation wave for modulating the beam pulses from the gain module. U.S. patent application Ser. No. 08/593,961, filed Jan. 30, 1996, titled Laser Pulse Profile Control By Modulating Relaxation Oscillations, assigned to the assignee of this application, and herein incorporated by reference, provides a more detailed discussion of a modulator for a diode-pumped solid state diode slab laser.
To provide for selective polarization of the light beam for various applications, the laser must be designed to allow the operator to selectively insert and remove the polarizing unit into and out of the beam path in a convenient manner. When the polarizer is inserted into the beam path to polarize the light, refraction of the light by the polarizing element causes the beam to deflect from the desired beam path. Therefore, the beam has to be returned or realigned to the output coupler, mirrors and other optical components in the laser each time the polarizer is put into or taken out of the beam path so that the beam is appropriately aligned with these optical components. Additionally, the polarizing element causes birefringence of the light beam that disperses or reflects a portion of the laser beam off of the polarizing element and out of the beam path. The dispersed portion of the light beam may impinge critical structural and optical components of the laser causing an undesirable heat build-up in the components. The heat build-up may cause dimensional changes of the components that may in turn produce beam distortion, unwanted beam steering and damage to the components. Further, the polarizer and/or modulator must be compact in design to accommodate the space constraints of the laser resonator cavity and laser packaging.
What is needed is a polarizer/modulator assembly that is compact in design, is readily connected to a solid state laser, provides for beam correction and tuning, and absorbs reflected light from the polarizing element and removes resulting heat. It is therefore an object of the present invention to provide such a polarizer/modulator assembly.